The sound speeds and densities of the 1-propanol + diethyl ether + 1-octanol ternary mixture and constituent binary mixtures, 1-propanol + diethyl ether, 1-propanol + 1-octanol, and diethyl ether + 1-octanol, have been measured at 298.15 K as a function of composition. Isentropic compressibilities, molar isentropic compressibilities, excess molar isentropic compressibilities, excess molar volumes, and excess sound speeds have been calculated from the experimental density and sound speed data. Excess molar volumes, excess molar isentropic compressibilities, and excess sound speeds of the binary mixtures were fitted to the Redlich-Kister equation. By using the free length theory (FLT), Schaaff's collision factor theory (CFT), Nomoto's relation (NR), Van Deal's ideal mixing relation (IMR), and Junjie's relation (JR), sound-speed values of the investigated mixtures were calculated. These values were compared with the experimental sound-speed results. © Springer Science+Business Media, LLC 2007.